1. Technical Field
The present invention is directed toward a check rail lock, and more particularly toward a check rail lock which is biased toward its open and locking positions.
2. Background Art
Check rail locks for locking double hung windows are well known in the art. These locks typically have a keeper mounted to the sash of the upper hung window, and a lock housing mounted to the sash of the lower hung window. The lock housing includes a cam which may be pivoted (typically through manual turning of an attached lever or handle by an operator) to either extend from the housing to grasp the keeper for locking, or to retract the cam into the housing clear of the keeper for unlocking.
Obviously, such locks do not serve their locking function if the cam is accidentally moved from its locking position (as might occur, for example, if the cam handle is accidentally bumped). Further, even partial movement of the cam toward the open position can reduce the security provided by the lock, since the taper of the lock cam can allow the window to be shaken by an intruder so as to conceivably further pivot the cam to the open position.
Similarly, the cam can damage the window if it is accidentally moved from the open position to the locking position when the window is open, since the projecting cam can then impact with the other window sash if the window position is thereafter changed (such impact and resulting damage can, in fact, be great given the fact that an open window is typically closed by rapid movement of the window (that is, by "slamming" the window).
Further, check rail locks such as described above are particularly susceptible to causing damage when used with certain types of windows if the lock is opened enough to clear the keeper but not enough to fully retract the cam into the housing (or is allowed to move back partially toward the locking position after it has initially been fully opened). For example, on double hung windows having a small horizontal distance between the glazing of the upper sash and check rail lock on the lower sash, the window glazing can be marked and otherwise damaged by the cam during movement if the cam projects even slightly from the lock housing. Similarly, in double hung windows having grill bars, a cam which projects only partially can still impact against the bars and mark or even break them during movement of the window.
Lock structures which have been used to ensure that the a check rail lock is properly disposed in its selected position are disclosed in Mosch U.S. Pat. Nos. 4,736,972 and 4,801,164, which locks use a spring washer with detents to provide a positive feel indicating that the lock has been properly positioned when fully moved to the selected locking or open position.
The present invention is directed toward overcoming one or more of the problems set forth above.